A gas diluter is an apparatus for thinning a concentration of a gas. There are a variety of objects requiring the gas diluter, however, for example, a fuel cell can be given as an application object thereof.
In the fuel cell, hydrogen introduced on an upstream side of a fuel electrode passes through a passage provided on the surface of the fuel electrode and diffuses downstream. In the fuel electrode, the hydrogen is separated into protons and electrons, wherein the protons diffuse toward an air electrode within the electrode and a polymer membrane, while the electrons reach the air electrode from an external circuit. Then, oxygen, the protons and the electrons are coupled due to reaction within the air electrode, thereby producing water. With continuation of this reaction, an electric current flows to the external circuit, and the electric power is supplied to a load.
In this case, the hydrogen supplied to the fuel electrode is not completely consumed, while part of the hydrogen passes through the passage on the surface of the fuel electrode and is, it follows, discharged from a discharge passage provided downstream of the fuel electrode. A known system is a fuel cell system, in which the downstream side of the fuel electrode is closed for restraining the discharge of the hydrogen. Further, another known fuel cell is a circulation type fuel cell, which circulates the hydrogen discharged from the downstream side of the fuel electrode toward again the upstream side.
In any type of fuel cell, due to a vapor produced as a contaminant of the reaction within the fuel cell, transmission of nitrogen toward the fuel electrode from the air electrode, etc., within the fuel electrode and the passage on the side of the fuel electrode, the fuel gas has a stepwise increase in a rate of impurity other than the hydrogen. If the impurity in the fuel gas increases, a density of the hydrogen brought into contact with the surface of the fuel electrode decreases, and hence a quantity of generation of the protons is reduced, resulting in a disabled state of sufficiently generating the electric power. Therefore, in the fuel cell system, generally, a discharge valve is provided downstream of the fuel electrode and is opened and closed at an interval of a predetermined time while detecting states of a power generation quantity, an output voltage, etc of the fuel cell, then the hydrogen gas is fed to the side of the fuel electrode, and the fuel gas containing the impurity is discharged (which will hereinafter be called “purging”). In this case, the hydrogen is required to be diluted so that the density of the hydrogen contained in the fuel gas to be discharged is equal to or less than flammability concentration.
Such being the case, for example, Japanese Patent Laid-Open Publication No. 2005-11640 discloses a technology of mixing the hydrogen gas of which to purge the fuel cell with a cathode off-gas, thus diluting the hydrogen. Further, another known technology is that in a dilution apparatus for diluting the hydrogen of which to purge the fuel cell, dilution air corresponding to a discharge hydrogen quantity is fed in so that a concentration of the hydrogen after being diluted does not reach the flammability concentration (refer to, e.g., Japanese Patent Laid-Open Publication No. 2004-127621).